Ditching techniques

[RadioSaigon]

There was a link to an interesting article (http://www.casa.gov.au/wcmswr/_assets/main/download/caaps/ops/253-1.pdf) published by Aerodynamisist in another thread (http://www.pprune.org/dg-p-general-aviation-questions/380891-life-jacket-ga-use.html) recently that struck me as worthy of further discussion. So rather than hijack JulieFlyGirl's thread, here we are.

The document (which I have linked to above) is excellent reference material, well worth the preservation of IMO... however, it does seem to contradict itself on what I consider to be a fairly major and very relevant point -should you ever be faced with a ditching.

Early in the document it states:

In ideal conditions you should always ditch into wind because it provides the lowest speed over the water and therefore causes the lowest impact damage. This process is effective provided the surface of the water is flat or if the water is smooth with a very long swell inside which the aeroplane will come to rest.

If the swell is more severe, including breaking waves, it is more advisable to ditch along the swell, accepting the cross wind and higher speed over the water, because this is preferable to ditching into the face of a wave and nosing in. Ditching into the face of a wave is very likely to cause extreme damage to the aeroplane and violent deceleration with severe implications for passengers and crew. The final approach will result in considerable drift which you must control to achieve the required tracking over the water. You must be careful to maintain sufficient airspeed to ensure that any action you take in controlling the path of the aeroplane does not lead to a stall. You must retain complete control of the aeroplane.

my emphasis RSthen tabulated towards the end of the document, we find:

0-6 knots
Glassy calm to small ripples
Height very difficult to judge above glassy surface. Ditch parallel to swell
7-10 knots
Small waves; few if any white caps
Ditch parallel to swell
11-21 knots
Larger waves with many white caps
Use headwind component but still ditch along general line of swell
22-33 knots
Medium to large waves, some foam crests, numerous white caps
Ditch into wind on crest or downslope of swell
34 knots and above
Large waves, streaks of foam, wave crests forming spindrift
Ditch into wind on crest or downslope of swell. Avoid at all costs ditching into face of rising swell

sorry, couldn't be stuffed re-tabulating it allThose two extracts from an otherwise excellent document appear to me to be absolutely contradictory. Dangerous play, especially considering this information is provided by the Regulator and may in some cases form a part of an approved Ops Manual or SOP!!!

Obviously, I have my own opinion of how these events would be handled -and that is pretty much in-line with what is contained within the 1st quote above: lower wind/water conditions, into wind; stronger wind/higher water conditions, parallel to swells and suck-up the x-wind.

I've been peripherally involved in one ditching. The aircraft was successfully and very professionally ditched, everyone survived the event and evacuated the aircraft, only for 1/2 of those aboard to subsequently lose their lives partially due to a lack of suitable survival equipment aboard but more IMO due to a bungled SAR effort, pissing contests and turf-wars.

I'm interested in what others opinions are of the document presented, techniques preferred and what SAR plans your company may have in-place in the event of a ditching.

[werbil]

RadioSaigon,

The next paragraph states:

In extremely windy conditions, greater than 20 knots for light aeroplanes with low stalling speeds or 30 knots or more for heavy aeroplanes with high stalling speeds, it may be worth ditching into wind to gain the large reduction in speed over the water. Aim to touchdown on the receding face of the swell. You may need to compromise between the beneficial effects of wind and the problems of swell. Advice on judging wind speed is provided at the end of this CAAP.


Which ties in nicely with the table at the end of the document.

Whilst I have never ditched, I do have nearly a couple of thousand water landings in what is classed as open water. Water is like concrete at 40 knots even with hulls that are designed to slice through the waves. Crossing a swell of the wrong wavelength will launch you back into the air with insufficient airspeed to fly - and the aircraft may very well slams back into the face of another wav.

IMHO, the only ideal water conditions are a good ripple on the surface with no swell. If there is swell you generally need to parallel it - which can be problematic in glassy conditions as you cannot see the swells. Obviously, when the wind speed approaches your stall speed facing directly into the wind should result in a softer ditching.

Better information can be found at http://www.faa.gov/airports_airtraffic/air_traffic/publications/atpubs/aim/Chap6/aim0603.html (http://www.faa.gov/airports_airtraffic/air_traffic/publications/atpubs/aim/Chap6/aim0603.html)
And from a survival perspective: http://www.uscg.mil/hq/cg5/cg534/SARfactsInfo/Ditching_WaterSurvivalAirventure08.ppt (http://www.uscg.mil/hq/cg5/cg534/SARfactsInfo/Ditching_WaterSurvivalAirventure08.ppt)
http://www.equipped.org/ditchtoc.htm (http://www.equipped.org/ditchtoc.htm) also contains a number or interesting articles.

[VH-XXX]

RadioSaigon, whilst I understand that it does seem to contradict itself, I think the answer to your question is in the definition of what the author calls "large waves."

If they are talking about "large" waves as in those out in the ocean, you're talking about HUGE swells WITH waves on them. Do you remember the conditions when the Helimed chopper from down in Victoria (made world wide headlines) rescued something like 12 sailors from the Sydney Hobart race? The waves were in excess of 35 feet. In these types of conditions the waves would be the least concern of yours in terms of their ability to inflict damage upon the aircraft, thus the comments about trying to not land into the face of swell, but rather down hill of it.

Quite simply I'd say your definition in your head of a wave and swell size are largely different to that of the author.

[RadioSaigon]

Good point Werbil -I should have read it further & more thoroughly :ok:

[Mr.Buzzy]

It's not you.......It's me.

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[Runaway Gun]

Does anyone have any good information about applying brakes (when in a fixed gear aircraft) before touching down on water? I'm in the belief that it helps the wheels to 'skip' over the water, rather than dig in immediately. (A bit like skimming a stone). Obviously it might only save you a few knots before the sudden stop, but every little bit of lost speed surely must help....